With Littrow2type external2cavity grating and temperature controlling , the spectral line width is compressed to be less than 1. 2 MHz (Δλ< 3. 5 ×10 - 6 nm) , while the original linewidth of the semiconductor laser is broader than 1200 GHz. Based on this , the system for measuring the amplitude and frequency of the microvibration with sinusoidal modulation is designed , detecting effect is good.